Vehicle window antennas that include embedded wires or silver print antennas in the rear window and windshield have been used in the prior art as an alternative to conventional whip antennas and roof mounted mast antennas. More recently, vehicle windows that are coated with an infrared reflective, thin metal film also have been used in connection with vehicle antennas. In the case of laminated glazing, the glass is formed of outer and inner glass plies that are bonded together by an interposed layer, preferably of a standard polyvinylbutyral or similar plastic material. The antenna may be screen printed on one of the inner surfaces of the glass plies using conductive ink such as silver paste or, alternatively, the antenna may be a thin conductive wire that is embedded in one of the surfaces of the interlayer.
There have been two ways to feed an antenna that is located in a laminated glazing—galvanic feed or coupling feed. The most common method has been direct feed by a galvanic connection through a flexible, flat connector. The flat connector comprises a conductor trace that is printed on a dielectric layer and covered with a dielectric tape. One end of a flat cable or film connector is soldered to an antenna wire or conductive printed pad and remains in the glazing structure when the window is laminated. The other end of the connector wraps over the outside edge of the glazing to connect to the exterior vehicle electronics.
Another method for connecting to antennas that are located in a laminated glazing has been a coupling feed. The coupling feed eliminates the need to solder the antenna to a connector or to pass a connector beyond the perimeter edge of glass to feed the antenna. For example, U.S. Pat. No. 8,077,100B2 to Baranski discloses an antenna coupling apparatus that transfers the antenna signal from an antenna wire situated inside laminated glass to a connector on an exterior surface of the glass. However, the Baranski antenna connector is based on transmission line coupling theory so that it cannot meet wide frequency band requirements such as for TV antennas that have as many as five frequency bands.
For efficient performance, the impedance of an antenna must be matched to the impedance of the transmission line that carries signals to and from the antenna. Any mismatch in impedance between the antenna and the transmission line will increase the standing wave that is present on the transmission line when transmitting or reduce the signal present on the transmission line when receiving. Such impedance matching must occur physically at the point of interconnection between the laminated glass antenna and a coaxial cable or an antenna amplifier input. Preferably, the impedance matching occurs in the FM, TV or other operating frequency bands where the input impedance is often 50Ω. WIPO Patent Application WO/2012/136411 to Bernhard discloses a flat antenna connector with a conductive shield on top of the antenna trace to increase capacitive coupling to the ground to improve signal transmission and reduce interference. The coupling capacitance acts as a high pass filter that improves the TV antenna performance at the UHF band (470 MHz-860 MHz). However, that design tends to degrade antenna performance at the lower frequency band such as the TV VHF band from 47 to 240 MHz.
With rapid growth in the demand for vehicle electronics, more and more antennas are being integrated to vehicles. Even though traditional mast or whip antennas have provided satisfactory performance in the past, often they are no longer preferred because they are considered to detract from vehicle aesthetics. With a greater number of antennas being integrated into window glazing, it was seen that there was a need in the prior art for an antenna connector that provided impedance matching to the laminated glass antenna. Such an antenna would be advantageous in comparison to a standard antenna connector.